During the past year, a major part of our efforts were devoted to the study of a newly discovered lymphotropic papovavirus (LPV) isolated from lymphocyte cultures of an African green monkey. This virus, belonging to the polyomavirus genus replicates exclusively in continuous lines of lymphoblastic cells. Serologic surveys indicate that similar viruses infect virtually all primates including humans. Because of the presence of defective particles in the original stock, the DNA of the virus was molecularly cloned using the plasmid vector pBR322. Analysis of 20 clones revealed the majority consisted of shorter length DNA molecules which were non-infectious. The longer DNA molecules were infectious and resulted in the production of high-titer, non-defective stocks of LPV. Using these new pools of LPV, we have established that the virus is not a strictly B-lymphotropic virus and can replicate in some lines of T-lymphocytes. A physical map of the LPV DNA has been constructed based on restriction endonuclease analysis of the cloned, non-defective DNA.